Transistorized ignition system for gas turbine engines

ABSTRACT

An ignition system for a gas turbine engine that includes a 2transistor oscillator which utilizes a transformer and requires only a spark plug in the secondary of the transformer to ignite fuel in the turbine.

United States Patent 91 [111 3,731,143 Thakore [4 1 May I, 1973 s41 TRANSISTORIZED IGNITION SYSTEM 3332,32 7/1328 Slit 0n ..31s 2o9 T 3,3 7 1 8 issen ..315/209 T FOR S TURBI NE ENGINES I 3,407,795 10/1968 Aiken et a1 ..315/209 T [75] Inventor: Kaushik H. Thakore, Sidney, NY. 3,424,142 l/i969 Nilssen et a1 ..315/209 T 3,478,249 11 1969 .1 k .315 209 T Assigneel 3121 WP Smlthfield, 3,531,737 9i1970 "riai m .315/209 1" 2 Filed: 25 1972 Primary Examiner.1ohn Kominski Attorney-Raymond J. Eifler et a1. [21] Appl. No.: 229,333

[57] ABSTRACT [52] U.S.'C1. ..3l5/209 T, 331/111 An ignition system for a gas turbine engine that in- [51] Int. Cl. ..H03k 3/30 cludes a 2-transist0r oscillator which utilizes a trans- [58] Field of Search ..315/209 T; 331/1 11 former and requires only a spark plug in the secondary of the transformer to ignite fuel in the turbine. t d v i [56] References e 4 Claims, 2 Drawing Figures UNITED STATES PATENTS 3,368,540 2/1968 Ault ..315/209 T PATENTEDMY' H 3,731,143

FIGURE 2 IGNITION CIRCUIT SPARK GAPI TURBINE ENGINE \2 FIGURE l TRANSISTORIZEI) IGNITION SYSTEM FOR GAS TURBINE ENGINES BACKGROUND OF THE INVENTION This invention relates to an electrical spark generating apparatus for gas turbine engines and the like.

Much difficulty has been experienced in providing a simple ignition system of small size, weight and with a minimum of components which will function satisfactorily to ignite so-called jet and gas turbine engines under all operating conditions. One example of a previous ignition system for a turbine engine is disclosed in US. Pat. No. 2,651,005 entitled Electrical Apparatus to T. Toghola, issued Sept. 1, 1953. However, this type of device utilizes a vibrator to create the oscillations that cause an electrical discharge across a spark gap to ignite fuel in a turbine engine. The disadvantages of such a system are (1) the short mechanical life of a vibrator, (2) the short life of the battery used to drive the vibrator because the vibrator uses so much power,

and (3) the cost of the entire circuit.

SUMMARY OF THE INVENTION This invention provides a simple and reliable transistorized ignition system for an automobile gas turbine engine.

The ignition system is characterized by a 2-transistor oscillator circuit that receives power from an automobile battery and applies it to a step-up transformer that has its secondary winding connectedto a spark gap discharge device that sparks at the frequency rate of the oscillator to ignite fuel in the turbine engine.

In one embodiment of the invention the ignition system for an automobile gas turbine engine comprises: a battery for supplying a DC voltage; a transformer having a primary winding and a secondary winding, with the secondary winding connected across a spark gap discharge device for igniting fuel in the engine; and

a transistorized oscillator circuit that is connected to g the battery and the primary winding of the transformer to periodically interrupt current from the battery to the primary winding whereby the oscillating current causes periodic electrical discharges across the spark gap device to ignite the fuel in the turbine engine. The circuit described provides high energy output pulses at the spark discharge device while requiring a low input voltage equal to the automobile battery voltage. The circuit is further capable of operating under short or open circuit conditions at the secondary winding of the step-up transformer.

Accordingly, it is an object of this invention to provide a battery-powered transistorized ignition system for an automobile gas turbine engine.

It is another object of this invention to provide a transistorized ignition system for a gas turbine engine that requires only a spark gap discharge device in the secondary winding circuit of a step-up transformer.

It is still another object of this invention to provide a transistorized ignition system for a gas turbine engine that has a minimum amount of components and preferably no more than two transistors.

It is still another object of this invention to provide a relatively inexpensive ignition system for a gas turbine engine.

A still further object of this invention is to provide a novel simplified ignition or spark-producing system which is useful for igniting automobile gas turbine engines.

Another object of this invention is to provide an electrical apparatus for creating electrical sparks or arcs that are adapted for igniting combustible materials.

Yet another object of this invention is to provide a transistorized ignition system for a gas turbine engine that is capable of operating under open circuit and short circuit conditions in the secondary circuit of the step-up transformer without damage to the remaining components of the ignition circuit.

It is yet another object of this invention to provide a constant power ignition system whereby regardless of variations of input voltages within a predetermined range of 824 volts the output power remains constant.

The above and other objects and features of the invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings and claims which form a part of this specification.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 11 is a block diagram of an ignition system for an automobile turbine engine.

FIG. 2 is a schematic diagram of a battery-powered transistorized ignition circuit that accomplishes the objects of this invention.

DETAILED DESCRIPTION OF THE DRAWINGS Referring now to FIG. 1, there is shown a block diagram of an ignition system for an automobile turbine engine which includes an ignition circuit 1 and a turbine engine 2 that includes a spark gap 40 therein for igniting the fuel fed to the engine.

FIG. 2 is a schematic diagram of a preferred embodiment of the ignition circuit 1 shown in FIG. 1. The source of electrical energy for the circuit is a battery 3 which is an ordinary automobile battery or a DC power supply having a voltage between 8 and 24 volts. The switch 5 is operable to connect and disconnect the battery to the circuit and is preferably a part of or associated with the ignition switch of an automobile. The spark gap discharge device 40 is a spark plug or the like which receives energy generated by the transistorized circuit and transformer. This causes a plurality of electrical discharges across spark gap 40 which occur at the same frequency rate as the oscillations in the primary portion of the transformer 30.

The first portion of the oscillator circuit includes a resistor 11 in series with the emitter of transistor 10 which has its collector in series with resistor 12 and its base in series with resistor 15 and diode 23. Blocking diode 23 is connected to the collector of transistor 20. The collector of transistor 10 is connected to the base of transistor 20 through lead 21 to provide a base current (drive) to transistor 20 when transistor 10 is conducting.

The resistor ]lI, the transistor 10 and the diodes 13, 14 are connected in the configuration shown to form a constant current regulator. This provides a constant current during increasing input voltages. The constant current output of this configuration provides the base current drive through lead 21 for transistor 20. Hence the base current of transistor 20 is fairly constant over the entire input voltage range. Since the collector current of transistor 10 is relatively constant, the ON time of the transistor 20 will decrease as the input voltage increases. Since the ON time of transistor 20 decreases as the input voltage increases, the input average current will also decrease if the OFF" time of the transistor 20 is constant. In this system the OFF" time of transistor 20 is a function of the ratio of the inductance of the secondary winding 32 of the transformer 30 to the resistance of the secondary winding 32 and voltage drop across the spark discharge device 40. The OFF time (T) may then be expressed by the following equation:

where:

L Inductance of the secondary winding 32 R, Resistance of the secondary winding 32 Ln Natural log a Initial current in the secondary winding 32 when the energy in the transformer 3l begins to discharge through the spark gap device 40 Since these parameters are fixed for a particular transformer and a particular spark plug, the turnoff time will be constant. Similarly the ON time may be expressed by the following equation:

where:

L, Inductance of primary 1,, Peak input current E Battery voltage OPERATION When switch 5 is closed the battery 3 applies electrical power to the circuitry causing capacitor 7 to charge through diode 13. The capacitor eventually attains the voltage equal to the battery voltage less the forward voltage drop of the diode 13. A current flows from the base of transistor 10 through resistors 11, and 16 to ground 4. This turns transistor 10 ON which permits a collector current to flow to ground through resistor 12 and through lead 21 to provide a base current to transistor 20, thereby turning transistor ON. When transistor 20 is ON, current from the battery 3 flows through the primary winding 31 of'transformer 30 and through the collector and emitter of transistor 20. With transistor 20 ON a linearly rising current begins to flow through the primary winding 31 of the transformer 30. Due to the inductance of the primary winding this current develops a constant voltage (approximately equal to the input voltage) across the primary winding 31 of the transformer 30. This voltage across the primary 31 causes diode 23 to conduct ON" and causes more current to flow through resistor 11 and the emitter-base junction of transistor 10. This causes transistor 20 to saturate quickly. A linearly rising current flows through the primary winding 31 and transistor 20 until the current reaches a peak value equal to the current through the base of transistor 20 times the gain of the transistor, at which time the transistor 20 comes out of saturation. When transistor 20 comes out of saturation the voltage across the transistor 20 increases and the voltage across the primary winding 31 will drop toward zero. As the voltage across the transistor 20 increases, it charges capacitor 7 through resistor 22. When the capacitor 7 charges to a voltage that overcomes the base voltage on transistor 10, the transistor 10 will stop conducting. This removes the current flowing in lead 21 to the base of transistor 20, turning transistor 20 OFF." Transistor 10 stays OFF as long as the voltage across the transistor 20 is high. During the OFF" time the voltage across the transistor 20 is approximately equal to the voltage across the spark gap divided by the turns ratio of the transformer 30 plus the voltage of the battery 3. Turning transistor 20 OFF results in a sudden decrease of the current flowing through the primary winding 31 and collector of transistor 20. During this time the rate of change of current (di/dt) becomes sharply negative, the high voltage induced in the secondary winding 32 of the transformer 30 also reverses, and the secondary winding 32 becomes a current source. The high voltage produced by the secondary winding causes an electrical discharge across the spark gap device 40 and the energy stored in the transformer 30 is dissipated in the electrical discharge in the spark gap discharge device 40.

When the energy stored in the transformer 30 is delivered to the spark discharge device 40, the current in the secondary winding 32 goes to zero. Simultaneously, a current starts to flow through resistor 11, emitter-base junction of transistor 10, resistor 15 and resistor 16, turning transistor 20 ON. The capacitor 7 discharges through resistor 22 and collector emitter junction of transistor 20 until the voltage of the capacitor 7 reaches the battery voltage 3 minus the voltage drop across diode 13. The circuit is now in a state to repeat the above-described cycle.

In one satisfactorily operable system the ignition system described in FIG. 2 had the values or were of the types indicated below:

battery 3 8-24 volts DC capacitor 7 .15 microfarads 50 volts diodes l3, 14, 23 1N645 resistor 11 8.5 ohms 1 watt resistor 12 82 ohms -0.5 watt resistor 15 1.5 K ohms -0.5 watt resistor l6 10 K ohms 0.5 watt resistor 22 1.5 K ohms -0.5 watt transistor 20 (NPN) TIP 305$ transistor 10 (PNP) TIP 30A transformer 30 primary I tums--N0.l8

secondary 18,000 turns-No.40 Bendix Part No. 10-372561-1 single pole Z-contact switch 5 While a preferred embodiment of the invention has been disclosed, it will be apparent to those skilled in the art that changes may be made to the inventions as set forth in the appended claims, and in some cases certain features of the invention may be used to advantage without corresponding use of other features. For example, different types of semiconductors or solid state control devices may be substituted for the types illustrated. Accordingly, it is intended that the illustrative and descriptive materials herein be used to illustrate the principles of the invention and not to limit the scope thereof.

Having described the invention, what is claimed is:

1. In combination with a gas turbine engine of the type having a spark gap for igniting fuel in the engine and an ignition circuit for producing an electrical discharge at the spark gap, the improvement wherein the ignition circuit comprises:

a source of DC energy; a transformer having a primary and a secondary winding, said secondary winding connected across said spark gap device;

a source of DC electrical energy;

a transformer having a primary and a secondary winding, said secondary winding connected across the spark gap;

switching means connected between said DC energy 5 switching means connected between said direct cursource and the primary winding of said transrent source and the primary winding of said transformer for connecting and disconnecting said DC former for connecting and disconnecting said energy source to and from said transformer; and direct current source to and from said transformer;

transistorized switching oscillator means connected and between said direct current source and the primal0 transistorized switching oscillator means connected ry winding of said transformer to periodically inbetween said direct current source and the primaterrupt current flow from said source through said wmhhg of sald tmhsfonher to Penodlcahy primary winding, said transistorized switching tehrupt h h flow h e e thmuh f oscmatorincluding: primary winding, said transrstorized switching a first transistor having collector and emitter teroselhator {hehldmgi minals connected in Series with the primary wind a first transistor having collector and emitter tering of said transformer, said transistor having alhhhals eehheeted m Sehes h e phmary wlhd' ternate conductive and nonconductive intervals to mg of sale Sald e havmg periodically interrupt the current flowing from the ternate conductive and nonconductive intervals to primary winding of Said transformer. periodically interrupt the current flowing from the a first voltage divider network connected across said pnmary fh of Sale thahsformer;

first transistor and the primary winding of said a first voltage divider network connected across said transformer, said first divider network including first "ahslstor f the Ph Wmdmg of e first and Second series connected diodes com transformer, said first divider network including nected in series to first and second series confirst h seeohd Senes connected e nected resistors. nected in series to first and second series conenergy storage means connected between the juncnected reslsmrs 7 tion between said diodes and the emitter of said energy Storage me Fohheeted between the J e first transistor. tion between said diodes and the emitter of said diode means connected between the junction first trahslstor;

between said resistors and the collector of said first hode meahe cohhected between the luhehoh transistor. between said resistors and the collector of said first a resistor connected between the junction between hahslstoh said diodes and the collector of said first transistor; 3 e e connected between the h h between a second voltage divider network connected across sale modes and theeoheetor of Sale trahslstor;

said first transistor and the primary winding of said a seeohd voltage chvder hetwerk eohheehed zeroes transformer, said second voltage divider network first trahsletor and the Phmary Yh of Sale including a second transistor having a fourth reh e f network sistor connected in series with its collector, a fifth t udmg a Second transistor having a fourth reresistor connected in series with its emitter and connected senes whh he collector a fifth having its base connected to the junction between resistor connected in series with its emitter and the diodes and resistors of said first voltage divider 'h base eohheeted Jhhehoh h e network. and the diodes and resistors of said first voltage divider means for connecting the collector of said second network and transistor to the base of Said first transistor means for connecting the collector of said second whereby when said Switching means connects said transistor to the base of said first transistor electrical source to said transformer, said whereby when sale 'h means connects f transistors are periodically rendered conductive, eleehheal Source 9 trahsformer h thereby periodically causing a discharge across transistors are periodically rendered conductive, said spark gap connected across the Secondary thereby periodically causing a discharge across winding ofsaid transformen said spark gap connected across the secondary 2. The electrical circuit recited in claim 1 wherein wmhhg ofeald h h h said source of electrical energy is a battery, d. The electrical circuit recited in claim 3 wherein 3. An electrical circuit for generating a plurality of sale sou'ce of eleemeal energy lshbattery' discharges across a spark gap which comprises: 

1. In combination with a gas turbine engine of the type having a spark gap for igniting fuel in the engine and an ignition circuit for producing an electrical discharge at the spark gap, the improvement wherein the ignition circuit comprises: a source of DC energy; a transformer having a primary and a secondary winding, said secondary winding connected across said spark gap device; switching means connected between said DC energy source and the primary winding of said transformer for connecting and disconnecting said DC energy source to and from said transformer; and transistorized switching oscillator means connected between said direct current source and the primary winding of said transformer to periodically interrupt current flow from said source through said primary winding, said transistorized switching oscillator including: a first transistor having collector and emitter terminals connected in series with the primary winding of said transformer, said transistor having alternate conductive and nonconductive intervals to periodically interrupt the current flowing from the primary winding of said transformer; a first voltage divider network connected across said first transistor and the primary winding of said transformer, said first divider network including first and second series connected diodes connected in series to first and second series connected resistors; energy storage means connected between the junction between said diodes and the emitter of said first transistor; diode means connected between the junction between said resistors and the collector of said first transistor; a resistor connected between the junction between said diodes and the collector of said first transistor; a second voltage divider network connected across said first transistor and the primary winding of said transformer, said second voltage divider network including a second transistor having a fourth resistor connected in series with its collector, a fifth resistor connected in series with its emitter and having its base connecTed to the junction between the diodes and resistors of said first voltage divider network; and means for connecting the collector of said second transistor to the base of said first transistor whereby when said switching means connects said electrical source to said transformer, said transistors are periodically rendered conductive, thereby periodically causing a discharge across said spark gap connected across the secondary winding of said transformer.
 2. The electrical circuit recited in claim 1 wherein said source of electrical energy is a battery.
 3. An electrical circuit for generating a plurality of discharges across a spark gap which comprises: a source of DC electrical energy; a transformer having a primary and a secondary winding, said secondary winding connected across the spark gap; switching means connected between said direct current source and the primary winding of said transformer for connecting and disconnecting said direct current source to and from said transformer; and transistorized switching oscillator means connected between said direct current source and the primary winding of said transformer to periodically interrupt current flow from said source through said primary winding, said transistorized switching oscillator including: a first transistor having collector and emitter terminals connected in series with the primary winding of said transformer, said transistor having alternate conductive and nonconductive intervals to periodically interrupt the current flowing from the primary winding of said transformer; a first voltage divider network connected across said first transistor and the primary winding of said transformer, said first divider network including first and second series connected diodes connected in series to first and second series connected resistors; energy storage means connected between the junction between said diodes and the emitter of said first transistor; diode means connected between the junction between said resistors and the collector of said first transistor; a resistor connected between the junction between said diodes and the collector of said transistor; a second voltage divider network connected across said first transistor and the primary winding of said transformer, said second voltage divider network including a second transistor having a fourth resistor connected in series with its collector, a fifth resistor connected in series with its emitter and having its base connected to the junction between the diodes and resistors of said first voltage divider network; and means for connecting the collector of said second transistor to the base of said first transistor whereby when said switching means connects said electrical source to said transformer, said transistors are periodically rendered conductive, thereby periodically causing a discharge across said spark gap connected across the secondary winding of said transformer.
 4. The electrical circuit recited in claim 3 wherein said source of electrical energy is a battery. 